Normal Menstruation and the Menstrual Cycle Flashcards
what defines the length of the menstrual cycle?
days between first day of bleeding > onset of bleeding in the next cycle
normal length of cycle?
21-35 days
usually 28 days
when is menstrual cycle usually most irregular?
around extremes of reproductive life due to anovulation and inadequate follicular development
length of follicular and luteal phase?
luteal phase = always 14 days
follicular phase = can vary from 10-16 days
what type of hormone is GnRH?
peptide
released from hypothalamus
how is GnRH released?
in a pulsatile manner
briefly describe HPO axis?
hypothalamus releases GnRH > anterior pituitary releases FSH and LH
- FSH acts on granulosa cells which secrete oestrogen and inhibin
- LH acts on theca cells which secrete androgens (androgens are converted to oestrogens by aromatase)
inhibin acts as negative feedback on anterior pituitary to reduce FSH production
oestrogen provides negative feedback to anterior pituitary and hypothalamus
how does oestrogen provide negative feedback?
mod oestrogen levels = negative feedback on HPO axis
high oestrogen levels (in absence of progesterone) = positive feedback on HPO axis
oestrogen in presence of progesterone = negative feedback on HPO axis
what are the 3 events in the ovarian cycle?
follicular phase
ovulation
luteal phase
follicular phase summary?
FSH rises in first few days > follicle grows in ovary > oestrogen produced by granulosa cells and via conversion of androgens from theca cells > oestrogen and inhibin act as negative feedback and decrease FSH release from pituitary > results in follicle with most FSH receptors (dominant follicle) getting most of the little FSH and continuing development while others degrade > dominant follicle continues producing oestrogen and inhibin which enhances androgen synthesis under LH control
what other hormones play a role in follicular phase?
inhibin and activin
IGF-1, IGF-2
what does inhibin do in females?
…produced by granulosa cells and feeds back to pituitary to downregulate FSH release
also enhances androgen release
what does activin do in females?
also produced by granulosa cells and pituitary
opposite to inhibin
works to increase FSH release
when does ovulation begin?
when the dominant follicle has fully grown and matured during follicular phase (average = 14 days)
what happens in ovulation?
lower FSH levels (due to negative feedback) forces LH receptors on the granulosa cells to compensate > oestrogen production increases until threshold where it then exerts positive feedback causing the LH surge > ovulation occurs around 12 hours after LH surge when the dominant follicle ruptures and releases oocyte
oestrogen increases up to threshold level during ovulation phase over a period of 24-36 hrs, what else happens during this time?
the LH-induced lutenization of granulosa cells causes progesterone to be produced
this progesterone adds to the positive feedback for LH secretion and causes a small periovulatory rise in FSH as well
what happens in the luteal phase?
remaining granulosa and theca cells in follicle after rupture and release of oocyte form the corpus luteum > corpus luteum secretes progesterone (beginning of secretory phase of endometrium)
ongoing pituitary LH release acts on lutenized granulosa cells to ensure supply of progesterone which stabilises endometrium for pregnancy > progesterone suppresses FSH and LH secretion to a level that wont cause any more follicle growth in that cycle
how does luteal phase progress in absence of pregnancy (no bHCG)?
corpus luteum will undergo luteolysis and regress
this causes decrease in progesterone levels
endometrium is no longer stabilised and therefore sheds causing menstruation
reduced progesterone, oestrogen and inhibin = removal of negative feedback on pituitary therefore FSH etc start to increase again stimulating follicle growth and starting the cycle again
when does progesterone peak?
7 days before start of next menses
clinical application of progesterone peak?
in assessing infertility and checking for ovulation
mid-luteal phase progesterone can be checked to determine if progesterone at level to cause ovulation?
the endometrium is under the influence of what?
sex steroids that circulate in females of reproductive age
3 endometrial phases?
proliferative
secretory
menstrual
proliferative endometrial phase?
exposure to oestrogen and progesterone results in cellular proliferation and differentiation in preparation for embryo
endometrium changes from a single layer of columnar cells to a pseudostratified epithelium with frequent mitoses
what happens in the secretory endometrial phase?
period of endometrial glandular secretory activity
endometrial glands become more torturous, spiral arteries grow and fluid is secreted into glandular cells and into uterine lumen
later, progesterone induces formation of temporary layer (decidua)
what is decidualisation?
formation of specialised glandular epithelium (decidua)
irreversible
apoptosis occurs if theres no embryo implantation
what happens in menstrual endometrial phase?
day 1
involves shedding of dead endometrium and ceases as endometrium regenerates
oestrogen and progesterone fall around 14 days after ovulation leading to a loss of tissue fluids, vasoconstriction of spiral arteries and distal ischaemia in endometrium
this causes tissue breakdown, loss of upper layer of endometrium (stratum functionalis) along with bleeding from remaining arteries seen as menstruation
how is haemostasis in endometrium different to other areas of body?
it does not involve process of clot formation and fibrosis
haemostasis more occurs due to multiple vasoconstrictors and vasodilators (including prostaglandins)
good drug to use for heavy menstrual bleeding and why?
NSAIDs such as mefenamic acid
inhibits prostaglandins causing vasoconstriction of spiral arteries
how does endoemetrial cycle relate to ovarian cycle?
prolfierative endometrial phase = ovarian follicular phase
secretory endometrial phase = luteal ovarian phase
